Asima mill

The Asima mill is an industrial universal mill for fine and ultra-fine grinding of a large number of different materials with a narrow particle size distribution.

development

The name Asima is derived from the name of the former manufacturer "Artur Simon-Maschinenbau", Cologne. It was developed as an air flow mill with the basic design features of the Lecher mill. The rotor and stator were cylindrical at the beginning, with the product entering from below. In the course of development, the rotor and stator were shaped conically. This made it possible to change the grinding gap in a simple manner by raising or lowering the stator.

This type of mill then came to the former company Fellner und Ziegler, Frankfurt, and later to Krauss-Maffei in Munich through market adjustments . The construction was completely revised there, and property rights were obtained for the term Asima . This type of mill is now manufactured by a large number of companies worldwide because of its special properties.

function

The rotor with U-shaped grinding tools in mostly four planes rotates in a stator housing. The stator housing is protected against wear by a corrugated grinding track. The ground material is fed in from above and falls onto the top plate of the rotor. Acceleration tools on the cover plate force the abandoned goods through radial acceleration into an orbit at a speed of approx. 125 m / s. The chambers formed by the four levels and by the U-shaped grinding tool cause a high speed in the gaps from chamber to chamber or from level to level. As a result, air eddies form at significantly different speeds. Due to the conicity of approx. 12 degrees, the mill acts like a fan and forces the sucked in air and thus also the ground material from the side with the smaller diameter to the side with the larger diameter. Since the rotor is vertical with its axis, the ground material is conveyed from top to bottom. The ground material with the air or the grinding gas (e.g. N2) is collected in an annular channel in the lower part of the housing. B. cyclone or filter.

Due to the conicity, the grinding gap can be easily adapted to the requirements of the ground material or the desired fineness. By grinding rings, occupied with the U-shaped grinding tools, which are kept smaller in diameter, z. B. make the upper grinding gap so the distance from the grinding edge of the grinding tools to the grinding path larger. The grinding gap can then be adapted to the grinding progress. Due to the earlier patented, advanced grinding edge of the U-shaped grinding tools, a material concentration in the gap between the levels is avoided. These grinding tools have established themselves and are used today by all manufacturers of such mills (eddy current and / or whirlwind mill).

The small and adjustable grinding gap is decisive for the final fineness of the ground material to be achieved. If a particle with a low mass is accelerated radially to a certain speed by the rotor, the air resistance in the grinding gap is decisive for the fact that the particle hits the grinding path of the stator with sufficient speed. With a particle (sugar) with a grain size of approx. 100 µm, the grinding gap should be set at approx. 0.5 mm. Only in this way can the particle be reduced to smaller z. B. 20 microns are crushed. Another decisive factor is the speed, number of revolutions and the rotor. This depends on the choice of material for the tool carrier rings and cannot be increased at will. When choosing the highest material quality for the rotor, the highest achievable speed is determined. This means that the grinding gap is of decisive importance for fine grinding.

Due to the high degree of turbulence and the different flow speeds between the vortex and the separating gaps, excellent fiberization is achieved.

operation area

This type of mill is suitable for grinding soft to medium-hard (approx. 3.5–4 Mohs ) materials. This type of mill has proven particularly useful in the processing of chemicals (pesticides, drugs, color pigments, etc.), plastics (thermosets or thermoplastics), minerals (limestone, chalk, gypsum, anhydrite, coating of fillers, etc.), food ( Sugar, rice, spices, dried vegetables, oats, soy, peanuts and cocoa to make porridge etc.), shredding of cellulose, wood, old newspapers to insulation material and in the rubber industry (selective grinding, separation of cords etc.).

literature

Hans Rumpf: Symposium comminution , Verlag Chemie, Weinheim

Web links

Short mention